The present invention relates to a permanent magnet embedment rotating electric machine in which a plurality of permanent magnets are embedded as magnetic poles inside a rotor that rotates in a stator around which windings are wound. The present invention also relates to a motor for a car air conditioner incorporating such a rotating electric machine and to an enclosed electric compressor.
A plurality of permanent magnets are embedded inside the rotor of this type of rotating electric machine so as to be adjacent to each other in the circumferential direction of the rotor. Two permanent magnets adjacent to each other in the circumferential direction of the rotor are set so that the magnetic poles are differently arranged. Since sudden magnetic flux density fluctuation occurs at a location (magnetic pole switching part) between the two adjacent permanent magnets, torque pulsation occurs and causes vibration and noise in the rotating electric machine.
Japanese Laid-Open Patent Publication No. 2001-69701 describes a motor having a rotor of which the radius becomes minimal at a location (magnetic pole switching part) between two permanent magnets that are adjacent to each other in the circumferential direction to suppress the torque pulsation. Further, the rotor has an outer circumference with a sinusoidal wave shape so that the radius of the rotor becomes maximal at the central portion (magnetic pole center) of each permanent magnet.
Japanese Laid-Open Patent Publication No. 2002-95194 describes a motor having a rotor of which the radius becomes minimal at a location between two adjacent permanent magnets (magnetic pole switching portion) in the circumferential direction and becomes maximal at the magnetic pole center. This is achieved by projecting the portion corresponding to the magnetic center on the outer circumference of the rotor outward into the shape of an arc.
Japanese Laid-Open Patent Publication No. 2002-136011 describes a motor having a portion corresponding to a magnetic pole center along the outer circumference of a rotor shaped as a Circumferential portion, which is coaxial with the rotor. Further, in the outer circumference of the rotor, the portion corresponding to two adjacent permanent magnets is groove-shaped.
In the motor disclosed in Japanese Laid-Open Patent Publication No. 2002-136011, the shape of the portion corresponding to the magnetic pole center of the outer circumference of the rotor is the circumferential portion that is concentric with the rotational axis of the rotor. Further, the part of the outer circumference of the rotor corresponding to the adjacent magnetic pole ends of the two permanent magnets has a groove shape.
Japanese Laid-Open Patent Publication No. 2004-260972 describes a motor in which a main magnetic pole portion and an auxiliary magnetic pole portion are alternately arranged in the circumferential direction. The outer circumference of the rotor is defined by alternately connecting a first curve portion, which corresponds to the main magnetic pole portion, and a second curve portion, which corresponds to the auxiliary magnetic pole portion. The curvature of the second curve portion is greater than the curvature of the first curve portion. An example using arcs for the first curve portion and for the second curve portion is described.
However, in the motors of Japanese Laid-Open Patent Publication No. 2001-69701 and Japanese Laid-Open Patent Publication No. 2002-95194, the location where the gap between the teeth of the stator and the outer circumference of the rotor becomes minimal is only the point-like portion corresponding to the magnetic pole center of the outer circumference in the side cross-section of the rotor. A torque constant (output torque per unit current) of the motor in the two publications thus becomes small compared to when the outer circumference radius of the rotor is constant.
In the motor of Japanese Laid-Open Patent Publication No. 2002-136011, the gap between the teeth of the stator and the outer circumference of the rotor greatly changes between the circumferential portion and the groove-shaped portion. Thus, the prevention of torque pulsation becomes difficult. When the groove is deep, the torque constant of the motor in Japanese Laid-Open Patent Publication No. 2002-136011 becomes further smaller than the torque constant of the motor in Japanese Laid-Open Patent Publication No. 2001-69701 and Japanese Laid-Open Patent Publication No. 2002-95194.
In the motor of Japanese Laid-Open Patent Publication No. 2004-260972, the steel portion between the main magnetic poles of the rotor is enlarged, as shown in FIG. 1 of the publication. That is, reluctance torque can easily be used. Therefore, a technique for reducing noise or vibration of the motor while suppressing the lowering of the average value of the output torque is disclosed.